Mechanisms and Longevity of Strain Localization during Dynamic Recrystallization of Olivine

橄榄石动态再结晶过程中应变局域化的机制和寿命

• 批准号: 1249737
• 负责人: Whitney Behr
• 金额: $ 22.81万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1249737&HistoricalAwards=false
• 关键词: Mechanisms; Longevity; Strain; Localization; during

This project investigates the role of grain size reduction by dynamic recrystallization in promoting strain localization in dry olivine aggregates using a suite of laboratory experiments coupled with detailed microstructural analyses. There are two primary goals of the project. The first is to identify the ways in which dynamic recrystallization can lead to localization under different conditions of stress, temperature, grain size, and strain magnitude. The processes that are most commonly proposed in the literature include a) geometric softening, b) a switch to grain size- sensitive deformation mechanisms, either diffusion creep or grain boundary sliding, and c) recovery by grain boundary migration. One or all of these mechanisms may contribute to the pronounced weakening observed in olivine under specific experimental conditions and in nature, and each should exhibit unique mechanical and microstructural signatures. The investigators will integrate detailed microstructural and mechanical observations over a range of experimental conditions, to systematically determine which of these mechanisms are dominant. The second goal is to examine the conditions under which dynamic recrystallization will result in permanent, as opposed to transient localization, by evaluating the role of syn-deformational grain growth. The project uses several unique ways of quantifying the role of grain growth in dynamically recrystallizing olivine aggregates, and of distinguishing between surface energy and strain energy driven grain boundary migration for a range of experimental conditions. The results of this research will have several important implications for geodynamics and mantle rheology, including the following. 1) The mechanical data will improve current deformation mechanism maps for dry olivine and can be incorporated into both large-scale mantle convection models and smaller-scale models of transient instabilities and mantle seismicity. 2) The processes identified as contributing to the development of olivine lattice preferred orientation can be input into models of olivine olivine lattice preferred orientation evolution and associated seismic anisotropy. 3) Distinguishing the conditions under which grain growth will counteract grain size reduction will allow evaluation of theoretical descriptions of the relationship between stress and grain size (the piezometric relationship). 4) The identification of microstructural criteria that are diagnostic of specific localization processes can be extrapolated to naturally deformed rocks and used to infer localization mechanisms and associated mechanical behavior of rocks under natural conditions.Understanding why deformation in Earth's rigid outer shell, the lithosphere, is commonly localized into faults and shear zones, rather than distributed over wide distances, is a fundamental question in geodynamics. These localized faults and shear zones are unique to planet Earth and are the reason parts of Earth exhibit rigid, plate-like behavior, in contrast to the more distributed deformation typically observed on other planets. Decades of observation of faults and shear zones where they cut the crust and upper mantle reveals that they are almost always associated with a significant reduction in grain size, which suggests that grain size reduction may be one of the most efficient mechanisms of localizing deformation. This project investigates mechanisms of grain size reduction in mantle rocks. Specific questions to be addressed include: under what conditions does grain size reduction lead to localization in mantle rocks? By what processes does the grain size reduction cause localization? And how long will the localization last on geological timescales? These questions will be addressed through integrated rock deformation experiments on olivine as well as detailed microstructural analysis of the experimentally deformed products.

该项目通过使用一套实验室实验以及详细的微结构分析来研究动态重结晶在促进干橄榄骨聚集体中应变定位中的作用。该项目有两个主要目标。首先是确定动态重结晶可以导致在压力，温度，晶粒尺寸和应变幅度的不同条件下定位的方式。文献中最常见的过程包括a）几何软化，b）转向晶粒尺寸敏感变形机制，即扩散蠕变或晶界滑动，以及c）通过晶粒边界迁移的恢复。在特定的实验条件和自然界中，一种或全部这些机制可能导致橄榄石中观察到的明显弱化，并且每种机制应表现出独特的机械和微结构特征。研究人员将在一系列实验条件下整合详细的微观结构和机械观测，以系统地确定这些机制中的哪些是主要的。第二个目标是检查动态重结晶将通过评估合成传染性晶粒生长的作用而导致永久性而不是瞬态定位的条件。该项目使用几种独特的方法来量化晶粒生长在动态重结晶橄榄石聚集体中的作用，并在一系列实验条件下区分表面能量和应变能驱动的晶界迁移。这项研究的结果将对地球动力学和地幔流变学有几个重要的影响，包括以下内容。 1）机械数据将改善干橄榄石的当前变形机理图，并可以纳入大规模的地幔对流模型和较小规模的瞬态不稳定性和地幔地震性。 2）被确定为有助于橄榄石晶格首选方向发展的过程可以输入到橄榄石橄榄石晶格的模型中，首选方向进化和相关的地震性各向异性。 3）区分谷物生长将抵消晶粒尺寸减少的条件将允许评估应力与晶粒尺寸之间关系的理论描述（打击关系）。 4）可以将特定定位过程诊断的微观结构标准鉴定为自然变形的岩石，并用于推断自然条件下岩石的定位机制和相关的机械行为。理解为什么在地球刚性外壳中的变形（岩石圈）通常将其定位于质量分配的质量分配的质量分配的是，岩石圈通常会构成岩石圈的质量分配。这些局部断层和剪切区是地球的独特之处，这是地球部分表现出刚性，板状行为的原因，与在其他行星上通常观察到的更分布的变形相反。几十年来观察断层和剪切区的观察，它们切开了地壳和上地幔，表明它们几乎总是与晶粒尺寸的显着减少相关，这表明晶粒尺寸减小可能是定位变形的最有效机制之一。该项目调查了地幔岩石中晶粒尺寸减少的机制。要解决的具体问题包括：在什么条件下，谷物尺寸降低会导致地幔岩石定位？通过减少晶粒尺寸的哪些过程会导致定位？该本地化将持续多长时间？这些问题将通过橄榄石的综合岩石变形实验以及实验变形产品的详细微观结构分析来解决。